To Cornell University climate professor Natalie Mahowald, the real scientific debate over man-made global climate change is over how far it will go, not whether it is happening.

"The real debate that people should be considering is how much they are willing to do to prevent changes in climate, and how much change in climate they are willing to tolerate," said Mahowald, who was the only upstate New Yorker listed as a lead author on last month's report from the United Nation's Intergovernmental Panel on Climate Change.

That report, the fifth issued by the U.N. since 1990, outlined and reaffirmed the long-standing global scientific consensus that emissions of greenhouse gases from burning of fossil fuels are warming the climate, melting glaciers and polar ice caps, causing oceans to acidify and sea levels to rise.

An associate professor of earth and atmospheric sciences at Cornell, Mahowald was lead author on the report's first chapter, which outlined the physical science that supports man-made climate change. She was among about 830 scientific experts from around the world who contributed to the report, and she also helped write chapter reports on aerosols and paleoclimate, which is the study of global climatic changes over long periods of time.

Among the latest IPCC report findings:

Warming of the climate system is unequivocal, and since the 1950s, many changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen and the concentrations of greenhouse gases have increased.

Evidence for human influence over climate change is growing. It is "extremely likely" that human influence has been the dominant cause of the observed warming since the mid-20th century.

Atmospheric concentrations of the greenhouse gases carbon dioxide (CO2), methane and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. CO2 levels have increased by 40 percent since preindustrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.

Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions.

"The results of this assessment are fundamentally similar to previous reports, with some more definitive statements because of additional data and scientific understanding," said Mahowald.

"We should focus the 'climate debate' on what to do about climate change instead of whether it is occurring," she said. "We should focus on what potential solutions to climate change would improve our lives in other ways, and thus should be encouraged no matter what."

For example, she said, alternative energy producers should have tax incentives similar to those long available to the coal and petroleum industry. "Improving energy efficiency can also reduce costs to companies and individuals, as well as reduce air pollution. These types of solutions should be pushed as much as possible, even as we debate more expensive and fundamental changes in business in the U.S., and whether we should and could implement them," Mahowald said.

Climate change is visible even to non-scientists — and to anyone who enjoys winter sports in New York, she said.

"As an avid cross-country skier, I am disappointed with the length of the snow season here in upstate: it was one to three weeks longer 30 years ago, according to records," Mahowald said.

Far to the north, sea ice in the Arctic is reduced during the summer to the point at which, for the first time, commercial ships can now navigate the Northwest Passage connecting the Atlantic and Pacific oceans, she added.

"The main conclusions are essentially the same as in previous reports," he said. "The climate model predictions are getting more reliable, so there are some statements in the new report that are even stronger than in prior reports."